Variable: A list of 'system directory designators' ASDF uses to find systems. A 'system directory designator' is a pathname or an expression which evaluates to a pathname. For example: (setf asdf:*central-registry* (list '*default-pathname-defaults* #p"/home/me/cl/systems/" #p"/usr/share/common-lisp/systems/")) This is for backward compatibilily. Going forward, we recommend new users should be using the source-registry.